1. Field of the Invention
The present invention relates to a complex terminal, and more particularly to a power control apparatus of a complex terminal.
2. Description of the Related Art
In general, a complex terminal receives electric power from a rechargeable battery detachably assembled with the complex terminal. The complex terminal may lose data when power supply from the battery to the terminal is stopped due to reasons such as separation or discharge of the battery. In preparation for unexpected interruption of power supply due to separation or discharge of the battery as described above, the complex terminal includes a separate auxiliary battery built in the terminal, which can supply electric power to the terminal in such a case.
FIG. 1 is a block diagram of a conventional complex terminal. Referring to FIG. 1, a conventional complex terminal may include a main battery 2 for supplying electric power, a phone module 4 for performing the function of a portable phone, and a PDA (Personal Digital Assistant) module 6 for performing the function of a personal information terminal or PDA. The PDA module 6 includes a PDA power supply 22, a first switch 24, a first voltage sensor 26, a second voltage sensor 28, a charger 32, an auxiliary battery 34, a second switch 36, a third switch 30, a DC/DC converter 38, a PDA controller 40, and a storage unit 42. The PDA module 6 is operated by the electric power supplied from the main battery 2.
The first voltage sensor 26 of the PDA module 6 detects voltage applied from the main battery 2. The first voltage sensor 26 directs the PDA module 6 to receive electric power from the auxiliary battery 34 instead of the main battery 2 when the detected voltage is lower than a predetermined value (e.g., 3.0 V). Here, while the power source to the PDA module 6 is switched from the main battery 2 to the auxiliary battery 34, the voltage applied to the PDA controller 40 becomes unstable.
FIG. 2 is a graph showing the voltage applied to the PDA controller 40 in a typical complex terminal. In the graph shown in FIG. 2, t1 represents a time point at which the voltage applied from the main battery 2 to the PDA controller 40 begins to be lowered due to discharge of the main battery 2 or separation of the main battery 2 from the complex terminal.
Referring back to FIG. 1, when the voltage of the electric power supplied from the main battery 2 becomes lower than a predetermined value (e.g., 3.0 V), the first voltage sensor 26 directs the first switch 24 and the second switch 36 to allow electric power to be supplied to the PDA controller 40 from the auxiliary battery 34 instead of the main battery 2. Specifically, when the voltage of the electric power supplied from the main battery 2 becomes lower than a predetermined value (e.g., 3.0 V) due to discharge of the main battery 2 or separation of the main battery 2 from the complex terminal, the first voltage sensor 26 directs the first switch 24 to connect the DC/DC converter 38 with the PDA controller 40, directs the second switch 36 to connect the auxiliary battery 34 with the DC/DC converter 38, and notifies the PDA controller 40 that the electric power is supplied to the PDA controller 40 from the auxiliary battery 34 instead of the main battery 2. When the voltage of the electric power supplied from the main battery 2 becomes lower than a second value (e.g., 3.2 V) due to discharge of the main battery 2 or separation of the main battery 2 from the complex terminal, the second voltage sensor 28 directs the third switch 30 to disconnect the charger 32 and the main battery 2 from each other, so as to prevent electric current from flowing backward from the charger 32 to the main battery 2.
When the auxiliary battery 34 and the DC/DC converter 38 are connected and the DC/DC converter 38 and the PDA controller 40 are connected, the PDA controller 40 can receive electric power from the auxiliary battery 34 instead of the main battery 2. However, during the process wherein the connection between the auxiliary battery 34 and the DC/DC converter 38 and the connection between the DC/DC converter 38 and the PDA controller 40 are established, the voltage of the electric power supplied to the PDA controller 40 becomes unstable. This is because the electric power supplied through the DC/DC converter 38 from the auxiliary battery 34 is not instantly supplied to the PDA controller 40. In other words, since the electric power is not instantly supplied to an input node of the PDA controller 40, the voltage has an unstable portion as designated by C in FIG. 2. This unstable voltage may cause misoperation of the PDA module 6 and loss of data in the complex terminal.